Method of modifying the properties of a metal matrix composite body

Abstract

PCT No. PCT/US93/06065 Sec. 371 Date Feb. 3, 1995 Sec. 102(e) Date Feb. 3, 1995 PCT Filed Jun. 25, 1993 PCT Pub. No. WO94/00610 PCT Pub. Date Jan. 6, 1994The present invention relates to modifying the properties of a metal matrix composite body by a post formation process treatment and/or a substantially contiguous modification treatment. The post formation process treatment may be applicable to a variety of metal matrix composite bodies produced by various techniques, and is particularly applicable to modifying the properties of a metal matrix composite body produced by a spontaneous infiltration technique. The substantially contiguous modification process may also be used primarily in conjunction with metal matrix composite bodies produced according to a spontaneous infiltration technique. Particularly, at least a portion of the matrix metal of the metal matrix composite body and/or the filler material of the metal matrix composite body is modified or altered during and/or after the formation process.

We claim: 
     
       1. A method of forming a metal matrix composite body, comprising: forming a permeable mass comprising at least one material selected from the group consisting of a second material and a precursor to a second material, said second material consisting essentially of at least one member selected from the group consisting of carbides, nitrides and oxides;   infiltrating molten matrix metal into at least a portion of said permeable mass to form an at least partially infiltrated mass comprising said at least one material embedded by said matrix metal;   thereafter heating said at least partially infiltrated mass to a temperature which is higher than the temperature at which the permeable mass was infiltrated;   reacting at least one component of said at least partially infiltrated mass with said material to form at least one reaction product in at least a portion of said at least partially infiltrated mass;   maintaining said higher temperature for a time sufficient to permit a desirable amount of said reaction to occur at said higher temperature; and   cooling said at least partially infiltrated mass.   
     
     
       2. The method of claim 1, wherein said permeable mass further comprises at least one filler material. 
     
     
       3. The method of claim 1, wherein said at least one material comprises at least two materials. 
     
     
       4. The method of claim 3, wherein at least two said materials comprise silicon nitride and boron carbide. 
     
     
       5. The method of claim 1, wherein at least a majority of said reaction occurs at said higher temperature. 
     
     
       6. The method of claim 1, wherein said reaction results in an increased volume of ceramic phases in said metal matrix composite body. 
     
     
       7. The method of claim 1, wherein said reaction produces a total net volume increase of said at least partially infiltrated mass. 
     
     
       8. The method of claim 1, wherein said reaction produces a total net volume decrease of said at least partially infiltrated mass. 
     
     
       9. The method of claim 8, further comprising supplying a reservoir of additional matrix metal to said metal matrix composite body during said heating and maintaining steps. 
     
     
       10. The method of claim 1, wherein said infiltration comprises at least one class of infiltration selected from the group consisting of spontaneous infiltration, pressure-assisted infiltration and vacuum-assisted infiltration. 
     
     
       11. The method of claim 1, wherein said infiltration comprises spontaneous infiltration. 
     
     
       12. The method of claim 11, further comprising an infiltrating atmosphere which is present at least at some point during said spontaneous infiltration step. 
     
     
       13. The method of claim 12, wherein said matrix metal comprises aluminum and said infiltrating atmosphere comprises a nitrogen-containing gas. 
     
     
       14. The method of claim 1, further comprising an atmosphere selected from the group consisting of an oxygen-containing atmosphere and a nitrogen-containing atmosphere which is present at least a some point during said heating and maintaining steps. 
     
     
       15. The method of claim 14, wherein said nitrogen-containing atmosphere comprises N 2 . 
     
     
       16. A method of forming a metal matrix composite body, comprising: forming a permeable mass comprising silicon nitride and a carbon source;   spontaneously infiltrating molten matrix metal into at least a portion of said permeable mass to form an at least partially infiltrated mass comprising said silicon nitride and said carbon source embedded by said matrix metal;   heating said at least partially infiltrated mass to a temperature which is higher than the temperature at which said permeable mass was at least partially spontaneously infiltrated;   reacting said matrix metal with said silicon nitride and said carbon source to form at least one reaction product in at least a portion of said at least partially infiltrated mass;   maintaining said higher temperature for a time sufficient to permit at least a majority of said reaction to occur at said higher temperature; and   cooling said at least partially infiltrated mass.   
     
     
       17. The method of claim 16, wherein said permeable mass further comprises at least one filler material. 
     
     
       18. The method of claim 17, wherein said at least one filler material comprises silicon carbide. 
     
     
       19. The method of claim 16, wherein said carbon source comprises at least one substance selected from the group consisting of elemental carbon and boron carbide. 
     
     
       20. The method of claim 16, wherein said matrix metal comprises aluminum. 
     
     
       21. The method of claim 16, further comprising an infiltrating atmosphere comprising nitrogen. 
     
     
       22. The method of claim 16, further comprising an air atmosphere which is present at least at some point during said heating and said maintaining steps. 
     
     
       23. The method of claim 16, wherein said higher temperature comprises a temperature of at least about 1200° C. 
     
     
       24. The method of claim 16, wherein said temperature at which said spontaneous infiltration occurs comprises a temperature in a range from about 800° C. to about 1000° C. 
     
     
       25. A method of forming a metal matrix composite body, comprising: forming a permeable mass of at least one material selected from the group consisting of a filler material and a preform;   mixing at least one second material into at least a portion of said permeable mass;   spontaneously infiltrating molten matrix metal into said permeable mass to form a metal matrix composite body in at least a portion of said permeable mass;   thereafter heating said spontaneously infiltrated mass to a temperature higher than that temperature at which said permeable mass was spontaneously infiltrated;   forming at least one reaction product in at least a portion of said spontaneously infiltrated mass; and   cooling said spontaneously infiltrated mass, at least a portion of which has been modified by said reaction product.   
     
     
       26. The method of claim 25, wherein said at least one reaction product comprises a reaction product of said matrix metal and said at least one second material. 
     
     
       27. The method of claim 25, wherein said at least one reaction product comprises a reaction product of said at least one second material and at least one member selected from the group consisting of said filler material and another of said at least one second material. 
     
     
       28. The method of claim 25, wherein said at least one reaction product comprises at least one member selected from the group consisting of a metallic material and a ceramic material. 
     
     
       29. The method of claim 25, wherein said matrix metal comprises aluminum and said at least one reaction product comprises an intermetallic compound. 
     
     
       30. The method of claim 25, wherein said at least one second material comprises at least one member selected from the group consisting of boron carbide and silicon nitride. 
     
     
       31. The method of claim 25, wherein an infiltrating atmosphere communicates with at least one of said permeable mass and said matrix metal at least at some point during said spontaneous infiltration. 
     
     
       32. The method of claim 31, further comprising the step of supplying at least one of an infiltration enhancer precursor and an infiltration enhancer to at least one of said matrix metal, said permeable mass and said infiltrating atmosphere. 
     
     
       33. The method of claim 32, wherein said infiltration enhancer precursor comprises a material selected from the group consisting of magnesium, strontium, calcium and zinc and said infiltrating atmosphere comprises an atmosphere selected from the group consisting of oxygen and a nitrogen containing atmosphere. 
     
     
       34. A method of forming a metal matrix composite body, comprising: providing a permeable mass comprising at least one filler material and at least one second material;   infiltrating a molten matrix metal into at least a portion of said permeable mass;   thereafter heating said at least partially infiltrated mass to a temperature higher than the temperature at which said molten matrix metal at least partially infiltrated said permeable mass;   maintaining said higher temperature for a time sufficient to permit at least some reaction of said at least one second material with at least one member selected from the group consisting of said filler material and said matrix metal; and   cooling said at least partially infiltrated mass.   
     
     
       35. The method of claim 34, wherein said reaction forms at least one reaction product in at least a portion of said at least partially infiltrated mass. 
     
     
       36. The method of claim 35, wherein a volume of said at least one reaction product is greater than the sum of the volumes of said second material and said at least one member with which said second material reacts. 
     
     
       37. The method of claim 35, wherein a volume of said at least one reaction product is less than the sum of the volumes of said second material and said at least one member with which said second material reacts. 
     
     
       38. The method of claim 37, further comprising contacting said at least partially infiltrated mass to at-least one source of additional matrix metal during said heating and maintaining steps. 
     
     
       39. The method of claim 37, wherein said volume of said at least one reaction product is greater than said volume of said at least one second material. 
     
     
       40. The method of claim 34, wherein said infiltrating comprises at least one technique selected from the group consisting of spontaneous infiltration, pressure infiltration and vacuum infiltration. 
     
     
       41. The method of claim 34, wherein said permeable mass is shaped as a self-supporting preform. 
     
     
       42. The method of claim 34, wherein at least a portion of said reaction occurs during said infiltrating step. 
     
     
       43. The method of claim 42, wherein at least a majority of said reaction occurs during at least one of said heating and maintaining steps. 
     
     
       44. The method of claim 34, wherein said second material comprises at least one member selected from the group consisting of carbides, nitrides and oxides. 
     
     
       45. The method of claim 34, wherein said second material comprises at least one member selected from the group consisting of boron carbide and silicon nitride. 
     
     
       46. The method of claim 34, wherein said second material comprises at least one member selected from the group consisting of a metal and a precursor to a metal. 
     
     
       47. The method of claim 34, wherein said second material comprises at least one member selected from the group consisting of carbon and a ceramic material. 
     
     
       48. The method of claim 34, wherein said second material comprises at least one oxide selected from the group consisting of copper oxide, iron oxide, nickel oxide, titanium dioxide, silicon dioxide and molybdenum trioxide. 
     
     
       49. The method of claim 34, wherein said permeable mass is substantially completely infiltrated prior to heating to said higher temperature. 
     
     
       50. A method for forming a metal matrix composite body, comprising: providing a permeable mass comprising at least one filler material and at least one precursor to a second material;   infiltrating a molten matrix metal into at least a portion of said permeable mass;   thereafter heating said at least partially infiltrated mass to a temperature higher than the temperature at which said molten matrix metal at least partially infiltrated said permeable mass;   maintaining said higher temperature for a time sufficient to form in at least a portion of said at least partially infiltrated mass at least one reaction product of at least one member selected from the group consisting of said filler material and said matrix metal; and   cooling said at least partially infiltrated mass.   
     
     
       51. The method of claim 50, wherein said precursor to a second material comprises a preceramic polymer. 
     
     
       52. The method of claim 50, wherein said precursor to a second material comprises at least one member selected from the group consisting of mullite and aluminum titanate.